ChrisS

I completed my engine (D16A6 replaced by ZC with intake from original engine) swap for my 91 CRX Si.

The engine fires and warms up. (seems to idle a little low, around 500 rpm; and maybe a little rougher than my D16A6. But, the guy I bought the ZC from said he put a bisimoto cam for a little more performance.)
Once it's warmed up, it will die at idle and won't fire without giving it gas.

My guess, so far Fast Idle Valve is functional. (the reason the car idles while warming up.)
and
Idle Air Control Valve isn't working correctly. (either electrical connection to it, the valve it self, or possibly both.)

A friend of mine said it could be the O2 sensor because that only starts working with the ECU once the engine is warmed up.

I should check the connection to the IACV maybe it got strained during all the shifting stuff around for the swap.

Another thing I'm considering is moving all the sensors/switches from my D16A6 engine block to the ZC engine block:
-2 prong above the oil filter(fan switch; does not seem to matter which wire is connected to which terminal)
-1 prong above the oil filter(oil pressure switch; working correctly)
-1 prong under the distributor(coolant temp sensor for the temp gauge in the cluster; working correctly)
-2 prong with plastic connector housing under the distributor (coolant temp sensor for the ECU; swapped the one from my D16A6 which was working correctly)
Maybe, one of these is bad on the ZC block.**

Any insight into fixing my idle once warmed up problem would be greatly appreciated.

Thanks,
Chris

**Note: Maybe, the fan switch on the back of the ZC is working correctly. But, the ECU sees that switch activate but doesn't see radiator's electric cooling fan kick in and either doesn't know what to do or cuts fuel to the injectors?

ChrisS

More info:
allowed it to idle until warmed up:
-disconnected the Idle Air Control Valve
result: engine stalls (IAC valve appears to be working, I think)
-turned on headlights or ventilator fan
result: engine stalls

On another forum someone mentioned a Electric Load Detector in the engine fuse box (I'll have to look into that and do a search through my electrical system; probably starting with all the grounds and battery connections)

No check engine light (so no codes).

ChrisS

More info:
battery = 12.53V with everything turned off
-drops to around 11V when cranking the starter
-once engine is running voltage jumps to 14.4V (alternator charging)
-don't have any way to do a load test or measure cold charging amps available on the battery (so, the battery still could have problems; it's almost 5 years old.)

Compression (no oil added to cylinders; engine a little under operating temp)(156psi listed the specification in the Haynes repair manual I have.)
#1 150
#2 155
#3 160
#4 150

I have to reset the ECU by disconnecting the battery for over 10 minutes for the engine to start cold. (I tried to start it when I got home tonight. No go until I reset the ECU.)
So, my guess is the ECU is getting bad data from a sensor and building an incorrect picture of how the engine is performing.

A tuner friend of mine suggested it might be the O2 sensor. (but, I using the same exhaust manifold and O2 sensor from the old working engine.)

After one idle session that dies when the engine gets close to operating temp, all the plugs are black with carbon (thin, flat black coating that's semi powdery).
[ATTACH=CONFIG]84018[/ATTACH]

I wiggled all the vacuum hoses while the engine was warming up (no change; so, I don't think any of those are causing a vacuum leak).

Next step maybe loosen and retorque the intake manifold (need to pickup a 12mm 6pt flex socket for this; maybe a 12mm crows foot too.)
The tricky nuts are bottom center, and the two near the PCV valve between cylinders #1 & #2.

Still without a car.
(the old D16A6 ran like a top. But, burned oil, leaked oil, and was getting tired.)

ChrisS

More info:

Ran an electrical bypass from the positive battery clamp to the main positive connection of the engine compartment's fuse box.
This seems to clean up some minor problems. (I'll replace the positive battery cable with one from honda once I get my main problem solved.)
The car idles smoother while warming up. I can turn on the headlights and vent fan to full and car still continues to idle during the warm up.

Tried switching the two wires that plug into the 2-prong switch assembly thermostat.
No affect on the main problem.

But, my main problem of:
Once the car warms to operating temperature it dies at idle and won't start without giving it gas still occurs.

Maybe, I'll swap the idle air control valve from the ZC intake I have and swap it with the one on the car. (it could be it's sticking or not moving enough.)

The next step is finding a good Honda specialist and having them fix the problem.

Note:
The idle adjustment screw on my car's intake is epoxied over (I think, it's California emissions that requires this. The ECU controls the idle with the idle air control valve.)
Otherwise, this problem would have been solved with a slight turn of a flat bladed screw driver a long time ago.

ChrisS

Further update:
-pulled the idle air control valve and cleaned the intake screen which was caked with carbon
-reinstalled it
-started and allowed car to warm up
-it stayed at idle (a little rough)
-I checked the ignition timing. It was off a bit.
-Set timing to spec.
Result:
It's better than before. But, not perfect. It can still stall occasionally at idle. (starting when warm requires a tiny bit of gas peddle which it shouldn't)
The new engine runs very well other than now relatively minor the stall problem.

Things to do:
-install new air filter (done)
-replace fram PCV valve with OEM Honda one (need to order part)
-replace positive battery connection with OEM Honda one (need to order part)
-check and adjust valve clearances (done)
-retorque intake manifold in three equal steps radiating out from the lower-center bolt (done. Didn't use the 12mm crowfoot wrench.)
-replace a bunch of 3.5mm vacuum tubing (in transit now; doesn't look like I need to replace it, see next reply)

-if fixing any of the potential vacuum leaks doesn't fix the stall problem, I'm probably going to replace the mild-performance bistmoto cam with the one from my original D16A6.

ChrisS

Retorqued intake manifold using 12mm 6pt flex socket, 3" extension, and inch-pound torque wrench; three equal rounds: 68, 136, and 204 in-lbs; final = 17 ft-lbs. per factory spec for the intake.
(note: had to pull fuel rail and move clutch cable, throttle cable, PCV valve & hose for access.)

Warmed up, check and adjusted ignition timing.
(maybe, one more timing check to do with "kill ECU adjustment" jumper in place; blue unconnected 2-wire plug near passenger door hinge.)

Basically, it looks like the problem is solved.
Now, I have to tweak the throttle cable slack a little bit (it's actually idling a little high now; factory spec is 10-12mm deflection; a simple one wrench fix).

ChrisS

The idle problem returned again. (pretty bad. it was stalling every time I came to a stop.)

I replaced all critical vacuum tubing and spark plugs. (no change problem still occurred)

I cleaned the MAP sensor's electrical connector pins.
This seemed to fix most of the problem. At least, on Wednesday night when I did the cleaning, it warmed to operating temp and stayed idling for 5 minutes. Very steady idle even turning on the head lights and ventilator fan to full didn't cause the engine to stall. It just picked up the extra load.

The drive in to work was stall free and idling was pretty stable/smooth.

On the drive back home, the car stalled once at idle about a mile from work (just about the time it was fully warmed up) and had a couple of times it almost stalled then the ECU caught the problem and opened the idle air control valve.

So, I'm still chasing a minor electrical problem.

I'll have the battery tested. (it's almost five years old. still cranks the engine just fine. but, maybe one of the cells is getting too weak)
Probably, replace the positive battery cable (starter/main positive connection to engine fuse box).
Maybe, replace the negative battery cable (main ground to car body and transmission).